RPL554 (9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one) is a dual PDE3/PDE4 inhibitor and is described in WO 00/58308, the entirety of which is incorporated by reference. As a combined PDE3/PDE4 inhibitor, RPL554 has both anti-inflammatory and bronchodilatory activity and is useful in the treatment of respiratory disorders such as asthma and chronic obstructive pulmonary disease (COPD). The structure of RPL554 is shown below.

The known method for producing RPL554 uses phthalimidoethyl alkylation chemistry followed by deprotection using hydrazine (see WO 00/58308). However, yields of RPL554 achieved by this route are relatively low and not well suited to large scale production. There are also problems associated with the use of the genotoxic deprotecting agent hydrazine to remove the phthalimide group. Furthermore, phthalimidoethyl alkylation agents are relatively expensive.
There is therefore a need to develop a new route for the production of RPL554. In particular, it is desirable to develop a process with an improved yield. There is also a need to avoid the use of genotoxic compounds such as hydrazine. In addition, it would be useful to develop a method which is more atom-efficient and avoids the need to use expensive alkylating agents.